While it has long been known that hydrogen gas can be generated by the reaction of acids with pure metals, efficient reactors for the controlled production of essentially pure hydrogen gas on an "as needed" basis have not been pursued. For the deep basing environment of the Intercontinental Ballistic Missile program, however, there is incentive to optimize the method and apparatus for generating hydrogen. In the deep basing environment, a network of tunnels, drifts, and raises will be located far enough underground that the base could survive a very large scale nuclear attack. A power source that can operate without access to outside resources, particularly without the need for combustion air, large scale cooling, or significant waste or by-product disposal, is essential to the survival and post-attack usefulness of such a base. The optimized method and apparatus of the present invention for generating essentially pure hydrogen gas on a demand basis uses dilute hydrochloric acid or another suitable halide acid to provide a non-toxic waste product, including soluble metal chlorides (or halides), and hydrogen gas that is suitable for use in a hydrogen-halide fuel cell. Storage of hazardous hydrogen gas is minimized. The acid is a by-product of the fuel cell operation.